There is no single grading scale here. What there is, is a short list of facts a buyer needs, and a habit of saying the uncomfortable one first.
For jewellery
Metal — hallmarked or not, and what the mark says. Wear to plating, if it is plated. Structure — thin spots on a band, a worn shank, a clasp that does not hold, links that have been replaced. Stones — present, loose, chipped, or missing. A missing stone is the single most common thing hidden by a careful photograph. Repairs — resizing, soldering, a replaced clasp. All normal; all to be declared. Cleaning — say if you cleaned it and how.
For watches
Running or not, and how long you tested it. Timekeeping, if you know it. Originality — dial, hands, crystal, crown, bezel, strap. Say what you believe is original and say how confident you are. Service history, or plainly that there is none. Case and crystal — scratches, dents, polishing. Box and papers — present, absent, or a replacement box.
The word to avoid
"Genuine", used as a guarantee about something you cannot show. It converts an honest sale into a claim you cannot defend. Describe what the piece carries — marks, papers, history — and let the buyer weigh it. Why trust is the product.
Untested is a real answer
"Untested, sold as seen" is a legitimate, common and perfectly sellable listing. It is also a defence: a buyer who paid untested prices cannot reasonably claim a tested result.
What is not legitimate is "untested" in the small print under a title that implies otherwise.
Questions people ask
Does a repair lower the value?
Usually a little; concealing it costs much more. Why naming the flaw raises the price.
How do I describe plating wear?
Plainly, with a photograph in neutral light, saying where it is worst.
Should I say a watch is "serviced" if a shop looked at it?
Only if you can say who and when. Otherwise say what was actually done.
More: condition words across every category, buying jewellery and watches.